1. Field of the Invention
This invention relates generally to venturis, eductors, aspirators, injector-mixers, and the like, and more specifically to an improved venturi design for aspirating and dissolving a first fluid into a second fluid.
2. Description of the Prior Art
Numerous venturi designs for aspirating and mixing fluids together are in common use in a wide range of commercial and industrial applications. Venturis operate in accordance with Bernoulli's principle, which states that pressure is inversely proportional to rate of flow. Therefore, to achieve suction or reduced pressure, the flow rate of a motive fluid is increased by funneling the fluid through a narrow venturi throat. An outlet through which an aspirated fluid is injected into the motive fluid is located in the region of lowest pressure (highest velocity) of the throat. Then, for efficient operation, the flow rate of the combined fluids must be reduced to at or near the original rate (thereby recovering momentum) without allowing turbulence or separation of flow from the walls to occur. Any deviation from laminar flow creates vibration and noise, as well as a backpressure which negates part of the suction, thereby requiring more pressure to drive the fluid through the orifice.
Prior art devices have accomplished the necessary reduction in the flow rate by using a diffuser pipe with a relatively long, conically expanding taper. This length can result in several disadvantages:
1. There are many applications where it would be desirable to have a venturi of much shorter overall length due to space considerations. PA0 2. A long venturi must be constructed from a large quantity of material, not only directly due to its length but also because increased length generally necessitates a larger overall diameter to maintain structural strength, and thus more volume or weight of material is required (volume being proportional to the square of the diameter). Since venturis are often used to aspirate and mix very corrosive fluids together, they frequently must be constructed of exotic (and expensive) materials. Many such materials, for example Teflon, have a low structural strength, thereby requiring a proportionally larger diameter and thus an even larger volume of expensive material for the venturi. Stronger inert materials such as Kynar and stainless steel are considerably more expensive and/or more difficult to fabricate into parts than is Teflon. PA0 3. In a long conical diffuser, the stream of aspirated fluid does not always mix well with the motive fluid. Even when it does mix, if for instance the aspirated fluid is a gas and the motive fluid is a liquid, the bubbles are usually not very small, and since they move together down the length of the long conical pipe, the bubbles have ample opportunity to recombine and grow even larger, which they inevitably do. This is often highly undesirable since the generation and maintenance of a very small bubble size is crucial to obtaining efficient solvation of an aspirated gas in a liquid. PA0 4. It is difficult to construct the entrance, throat, and exit portions of the venturi all in one piece (which construction is often desirable for corrosive media). PA0 5. It can be difficult to position the aspirator outlet within the venturi so as to provide symmetrical introduction and therefore optimum distribution of the aspirated fluid, and this becomes even more difficult when the entrance, throat, and exit portions of the venturi are all in one piece. PA0 1. the one-piece cylindrical cartridge body containing the entrance cone, the venturi throat, and the rear surface which defines the first side of a thin-sheet diffusion volume, with an optional short expansion cone between the venturi throat and the thin-sheet volume, and an optional concave radius at the outer edge of the rear surface which directs the exiting flow; PA0 2. the radial diffuser or end piece; PA0 3. the straight axial aspirator tube (with a symmetrical outlet centered coaxially in the motive flow through the venturi throat); and PA0 4. the aspirator tube support.
Additional problems with prior art venturis (which become more severely problematic when designing for corrosive media) include the following: